The invention relates to an electronic regulator circuit producing a reference voltage that varies with temperature. In particular, the regulator circuit includes a band-gap generator for supplying a power stage through an error amplifier and a comparator, with the error amplifier also receiving a regulated voltage. More particularly though not exclusively, the invention relates to a voltage regulator for automotive applications, and the following description is made with reference to this field of application for convenience of illustration.
As it is well known in this technical field, for voltage regulators to be used in motor alternators, a battery regulated voltage has to follow a specific pattern with temperature variations. Usually, this pattern can be represented by a polygonal curve of voltage plotted against temperature which changes in slope at predetermined breakpoints, as shown in FIG. 1, where the curve includes at least three segments.
This dependence of the voltage regulator on temperature is usually established inside the regulator circuit, using a reference which obeys a desired law, for instance as shown in FIG. 1, but is scaled in value by a factor K set by a voltage divider, for example.
More particularly, a conventional voltage regulator 1 is shown by way of example in FIG. 2, which uses a supply voltage VGO derived from an external source. Regulators of the kind shown in FIG. 2 commonly equip automobile vehicles having an alternator associated with their power plant. The alternator output voltage VGO, although much affected by noise, is often used to supply the less critical portions of the vehicle""s own electronic circuitry. These circuit portions, e.g., digital circuits and power stages, are indeed the most consumption-intensive ones.
The regulator 1 includes a band-gap regulator block 2 intended for generating a stable reference signal Vr from a supply line 3 presenting the voltage VGO. One example of a band-gap circuit is disclosed in U.S. Pat. No. 5,309,083 to Valeo Equipments Electriques.
The reference voltage signal Vr, also referred to as the set point signal, is supplied to respective inverting (xe2x88x92) inputs of an error amplifier 4 and an output comparator stage 5, when regulation is non-linear and provided through a relay. When regulation is instead achieved by a PWM signal, the inverting input of the comparator 5 will receive the PWM signal.
In either cases, both the error amplifier 4 and the comparator 5 are supplied by a voltage VGO line 3, and the output of the error amplifier 4 is connected to the non-inverting (+) input of the output comparator stage 5. A voltage divider 6 is provided between a SENSE line and a ground voltage reference GND. A voltage value Vs to be controlled is present on the SENSE line.
The signal Vs on the SENSE line is equal to K Vr, where K is the partition factor. For example, if the divider 6 is of a resistive type, a first resistor of unitary resistance is connected in series to a resistor of resistance (Kxe2x88x921). The interconnection node X between these resistors is connected to the non-inverting (+) input of the error amplifier 4 to deliver a voltage value given by the ratio Vs/K.
A regulation loop, which is not shown because it is conventional, will make the value of the signal Vs on the SENSE line K times greater than the reference voltage signal Vr. The regulator structure 1 described with reference to FIG. 2 may be operated in different regulating modes.
For example, the regulator 1 may be operated in a switching mode, a PWM (Pulse Width Modulation) mode, or in a relay type of non-linear mode. Such a structure is described, for example, in U.S. Pat. No. 5,703,476 assigned to the assignee of the present invention, and the entire contents of which are incorporated herein by reference.
Although in many ways advantageous and substantially achieving its objective, the above regulator structure is inadequate to allow a simulation of the curve of FIG. 1 to be obtained in any comparatively simple manner, with respect to all of the above regulating modes. In addition, none of the above-outlined approaches are economically advantageous, from both standpoints of power consumption and circuit complexity.
An object of this invention is to provide an integrated electronic circuit for regulating a reference voltage that varies with temperature. The integrated electronic circuit has structural and functional features such that it can be supplied by a voltage produced inside the circuit itself, thereby reducing the overall power consumption and improving the stability features of the generated reference voltage signal Vr.
The principle on which this invention stands is one of using, as a supply voltage, the controlled signal Vr of the SENSE line produced by the regulator circuit itself, and applying this supply voltage to a plurality of band-gap regulators substantially provided in a number equal to the number of segments of a polygonal curve to be tracked by the regulator characteristics.
Based on this principle, an object of the invention is achieved by providing an electronic regulator circuit that comprises a voltage divider having an input for receiving a regulated voltage, and an output for providing a divided regulated voltage. A plurality of band-gap generators are connected to the voltage divider, with each band-gap generator being supplied by the regulated voltage and having an input for receiving the divided regulated voltage. In addition, each band-gap generator may have an error amplifier and a comparator incorporated therein. The electronic regulator circuit may further include a logic network connected to a respective output of each band-gap generator, and an output of the logic circuit may be connected to a power stage.
The regulator circuit may further include a regulating loop for producing the regulated voltage. The plurality of band-gap regulators are substantially a same number as there are segments of a polygonal curve representing a desired pattern of the reference voltage as the temperature varies.
Each band-gap generator preferably comprises a current mirror having a first circuit leg and a second circuit leg, with the first and second circuit legs independently connecting a regulated voltage supply line to ground. The first circuit leg preferably comprises a transistor receiving the divided regulated voltage, and the second circuit leg preferably includes an output for connecting to the logic network.
Each band-gap generator preferably further comprises an inverter having an output connected to the logic network, and the plurality of band-gap generators are modularly connected in a circuit structure having an input connected to the voltage divider.